A positive electrode lithium supplementing agent, a preparation method and application thereof

Abstract

The application provides a positive electrode lithium supplementing agent and a preparation method and application thereof, and belongs to the field of lithium ion battery materials, and can solve the problems of a complicated preparation process, high energy consumption and no improvement on the battery side reaction of lithium iron oxide in the existing carbon coating method. The positive electrode lithium supplementing agent comprises a core containing a lithium supplementing material and a coating layer covering the core containing the lithium supplementing material, wherein the core containing the lithium supplementing material is doped or non-doped lithium-rich lithium iron oxide, the coating layer is a conductive polymer containing a sulfur load, the sulfur load is uniformly dispersed in the conductive polymer, the content of the sulfur load is 0.01-1 wt% of the positive electrode lithium supplementing agent, and the content of the conductive polymer is 0.5-10 wt% of the positive electrode lithium supplementing agent. The positive electrode lithium supplementing agent increases the material interface stability, improves the simplicity and universality of material application, reduces the occurrence of electrolyte side reactions, improves the long cycle stability of the battery, and simplifies the complexity of the battery preparation process.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, and particularly relates to a positive electrode lithium replenishing agent, its preparation method and application. Background Technology

[0002] With the continuous development of lithium-ion battery technology, the performance development of existing commercial lithium-ion battery systems (cathode-graphite-liquid electrolyte) has almost reached its limit, and improving energy density remains the top priority for future battery development. It is well known that during the first cycle of a lithium-ion battery, the formation of the SEI film on the negative electrode consumes approximately 7-10% of the active lithium. This means that some of the Li+ ions extracted from the positive electrode material are irreversibly consumed, leading to reduced battery capacity, lower coulombic efficiency, and poorer cycle performance. When using high-specific-capacity negative electrode materials, such as silicon-tin alloys, oxides like silicon oxide and tin oxide, or amorphous carbon negative electrodes, the negative electrode material, especially silicon-based negative electrode materials, will further consume Li+ ions, further exacerbating the consumption of the positive electrode lithium source and resulting in excessively low initial coulombic efficiency.

[0003] To further improve the energy density of lithium-ion batteries, replenishing active lithium has become an effective means of solving this problem. Currently, existing lithium replenishment methods include positive electrode lithium replenishment and negative electrode lithium replenishment. Negative electrode lithium replenishment involves the use of highly reactive metals such as lithium powder and lithium foil, which are too active and cannot be stored stably for long periods, thus increasing operational difficulty and production risks. Positive electrode lithium replenishment is simple and easy to operate; a small amount of positive electrode lithium replenishing agent can be added during the homogenization process of positive electrode preparation, and lithium replenishment can be achieved during the formation stage. The lithium replenishment process is safe and has good compatibility with existing battery manufacturing processes, thus having broad commercial application prospects. Currently, there are many types of positive electrode lithium replenishing agents researched and reported. Among them, Li5FeO4, due to its high specific capacity (theoretically 867 mAh / g), is considered to be the most effective lithium replenishing agent currently available. However, Li5FeO4... 4的 Li5FeO4 exhibits extremely poor conductivity and air stability; even contact with small amounts of water in the air at room temperature will produce lithium compound impurities, leading to decreased material performance and increased polarization. The high cost and difficulty in preparing Li5FeO4 materials hinder large-scale industrial production and application. Furthermore, the high delithiation voltage of Li5FeO4 (3.5-4.7V) necessitates modifications to formation conditions to achieve the desired specific capacity. It is well known that at higher voltages, transition metal elements, especially Ni in ternary materials, readily catalyze electrolyte side reactions, causing abnormal gas production and excessive gas generation, thereby deteriorating the battery's long-cycle performance. Therefore, the application of lithium-rich lithium iron phosphate (LiFeO4) also poses a significant challenge to the performance of existing commercial electrolytes.

[0004] However, existing methods for improving conductivity and air stability involve carbon coating, which requires thorough mixing of the lithium replenishment material and the coating source before high-temperature sintering, or the use of organic gases for high-temperature catalytic cracking to achieve carbonization. The preparation process is cumbersome and energy-intensive, and it does not address the side reactions of lithium ferrite batteries. Summary of the Invention

[0005] This invention addresses the problems of existing carbon coating methods, such as cumbersome preparation processes, high energy consumption, and failure to improve the side reactions of lithium ferrite in batteries. It proposes a cathode lithium replenishment material with a simple preparation process and high compatibility with air and processes, which increases the stability of the material interface, simplifies the complexity of battery preparation processes, improves the ease and versatility of lithium replenishment material application, reduces the occurrence of electrolyte side reactions, and enhances the long-cycle stability of batteries.

[0006] To achieve the above objectives, the present invention provides a positive electrode lithium replenishing agent, the technical solution of which includes a core containing lithium replenishing material and a coating layer covering the core containing lithium replenishing material. The core containing lithium replenishing material is a doped or undoped lithium iron ferrite, and the coating layer is a conductive polymer containing a sulfur-containing loading. The sulfur-containing loading is uniformly dispersed in the conductive polymer, the content of the sulfur-containing loading is 0.01-1 wt% of the positive electrode lithium replenishing agent, and the content of the conductive polymer is 0.5-10 wt% of the positive electrode lithium replenishing agent.

[0007] Preferably, the positive electrode lithium replenishing agent has the molecular formula Li5Fe. 1-x O4M x @S / P, where M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Ti, and Al, 0 ≤ x ≤ 0.5; S is a sulfur-containing loading material; and P is a conductive polymer containing a conjugated structure.

[0008] Preferably, the sulfur-containing loading material is at least one of elemental sulfur, polymerized sulfur, or sulfur-containing oxides, inorganic salts, organic salts, ester compounds, and sulfur-containing polymers; the conductive polymer is a conductive polymer containing a conjugated structure, and the conductive polymer is at least one of polyaniline, polypyrrole, polythiophene, PEDOT, polyacrylonitrile, polyacetylene, poly(p-phenylene oxide), polydopamine, and their derivatives.

[0009] In another aspect, the present invention provides a method for preparing the above-mentioned positive electrode lithium replenishing agent, comprising the following steps:

[0010] Iron source, lithium source and doped metal source are added to water in a certain proportion to form a uniform gel, and then the precursor powder is obtained by spray drying using a spray dryer.

[0011] The precursor powder was sintered at high temperature under inert gas conditions to obtain lithium iron ferrite core.

[0012] The lithium iron ferrite core powder, sulfur-containing precursor, polymer or polymer monomer are added to an organic solvent and polymerized in a high-pressure reactor. After filtration and drying to remove the solvent, a positive electrode lithium replenishing agent is obtained.

[0013] Preferably, the iron source is at least one selected from Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3·9H2O, FeCl3, and FeSO4; the lithium source is at least one selected from Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4, and CH3COOLi; and the doped metal source is an oxide, hydroxide, or inorganic salt containing at least one metal element selected from Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, and Al.

[0014] Preferably, the molar ratio of the iron source to the lithium source is (5.0 to 7.0):1.

[0015] Preferably, the inert gas is at least one of nitrogen, argon, and helium.

[0016] Preferably, the sulfur-containing precursor is at least one of elemental sulfur, sulfate, thiol, and sulfate ester, wherein the amount of sulfur-containing loading is calculated and determined based on the sulfur doped in the target cathode lithium supplement; the polymer monomer is at least one of aniline, pyrrole, thiophene, EDOT, acrylonitrile, acetylene, p-benzene, dopamine and its derivatives; and the organic solvent is at least one of anhydrous ethanol, acetonitrile, propanol, tetrahydrofuran, carbon tetrachloride, carbon disulfide, DMF, DMAC, and NMP.

[0017] Preferably, the high-temperature sintering temperature is 600-1000℃ and the sintering time is 2-40h; the polymerization reaction temperature is 80-300℃ and the reaction time is 2-20h.

[0018] The application of the above-mentioned positive electrode lithium supplement in this invention is that the positive electrode lithium supplement is used to prepare lithium-ion batteries, and the amount added is 0.5-5% of the mass ratio of the positive electrode active material.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0020] (1) The positive electrode lithium replenisher of this invention uses lithium-rich lithium ferrite with an anti-fluorite structure as the core and a conductive polymer loaded with S as the coating shell. The lattice defects of the lithium-rich lithium ferrite material are increased by metal element doping, which is beneficial to improving the lithium content. +The diffusion rate and internal conductivity of the particles within the material are improved; by coating the outer surface of the lithium replenisher core with a long-range conjugated conductive coating layer, the electronic conductivity of the material is enhanced, further reducing the lithium removal energy barrier; the conductive polymer has an organic conjugated structure, and the resulting dense coating layer can isolate moisture and CO2 in the air, increasing the stability of the material interface, thus significantly improving both lithium replenishment performance and processing performance.

[0021] (2) The S-containing loading material in the positive electrode lithium replenishment agent of the present invention can react directly or indirectly with the electrolyte and be converted into CEI film components that adhere to the surface of the cathode material, reduce the active sites of the cathode material, avoid the direct contact of transition metal elements with the electrolyte, thereby reducing the occurrence of electrolyte side reactions and improving the long cycle stability of lithium-ion batteries. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the positive electrode lithium replenishing agent provided in an embodiment of the present invention;

[0023] Figure 2 This is a SEM image of the positive electrode lithium replenishing agent provided in Example 1 of the present invention;

[0024] Figure 3 The image shows the EDS diagram of element C in the positive electrode lithium replenisher provided in Example 1 of this invention.

[0025] Figure 4 The image shows the EDS diagram of the positive electrode lithium replenishing agent O element provided in Embodiment 1 of the present invention;

[0026] Figure 5 The image shows the EDS diagram of the S element in the positive electrode lithium replenisher provided in Embodiment 1 of the present invention;

[0027] Figure 6 The image shows the EDS of Fe element in the positive electrode lithium replenisher provided in Example 1 of this invention;

[0028] Figure 7 The image shows the SEM image of the positive electrode lithium replenishing agent provided in Comparative Example 1 of this invention.

[0029] 1. Core containing lithium-supplementing material; 2. Conductive polymer; 3. Sulfur-containing loading material. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention provides a positive electrode lithium replenishing agent, its preparation method, and its application. The positive electrode lithium replenishing agent includes a core containing lithium replenishing material and a coating layer covering the core containing lithium replenishing material. The core containing lithium replenishing material is doped or undoped lithium-rich ferrite, and the coating layer is a conductive polymer containing a sulfur-loaded material. The sulfur-loaded material is uniformly dispersed in the conductive polymer, and the content of the sulfur-loaded material is 0.01-1 wt%, while the content of the conductive polymer is 0.5-10%. By using doping and sulfur-loaded polymer coating technology to perform dual modification on lithium-rich ferrite, the synergistic effect of the doping element and the coating layer improves the conductivity and interface stability of the resulting product, while simultaneously enhancing the battery's performance, especially its long-cycle performance.

[0032] The molecular formula of the positive electrode lithium replenishing agent of this invention is Li5Fe 1-x O4M x @S / P, where M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, and Ti, and 0 ≤ x ≤ 0.5. The sulfur-containing loading material can directly or indirectly form a CEI film, reducing the active sites of the cathode material, avoiding side reactions with the electrolyte, and thus improving the long-cycle stability of the lithium-ion battery. The sulfur-containing loading material is at least one of elemental sulfur, polymeric sulfur, or sulfur-containing oxides, inorganic salts, organic salts, ester compounds, and sulfur-containing polymers. The conductive polymer is a conductive polymer containing a conjugated structure. The conductive coating layer of the conjugated structure endows it with excellent electronic conductivity while isolating it from moisture and CO2 in the air, giving it good conductivity and air stability, thus significantly improving lithium replenishment performance and processing performance. The conductive polymer is at least one of polyaniline (PAn), polypyrrole (PPy), polythiophene (PTh), PEDOT, polyacrylonitrile (PAN), polyacetylene (PA), poly(p-phenylene oxide) (PPP), polydopamine, and their derivatives.

[0033] The preparation method of the above-mentioned positive electrode lithium supplement of the present invention includes the following steps:

[0034] Iron source, lithium source and doped metal source are added to water in a certain proportion, heated and stirred to form a uniform gel, and then spray dried using a spray dryer to obtain precursor powder.

[0035] The above precursor powder was sintered at high temperature under an inert gas and then cooled in the furnace to obtain lithium-rich lithium iron ferrite core.

[0036] The above-mentioned lithium iron ferrite core powder, sulfur-containing precursor, polymer or polymer monomer are added to an organic solvent and polymerized in a high-pressure reactor under closed conditions. After filtration and drying to remove the solvent, a positive electrode lithium replenishing agent is obtained.

[0037] In the above preparation method, the molar ratio of iron source to lithium source is 5.0 to 7.0:1. The amounts of iron source, lithium source and doped metal source are weighed according to the molar ratio of each element corresponding to the molecular formula of the positive electrode lithium supplement. In order to prevent the generation of impurities such as LiFeO2 due to Li volatilization under high temperature conditions, the lithium source is weighed in excess by 0.1-20% to ensure the purity of the sample. The iron source is at least one of Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3·9H2O, FeCl3, and FeSO4, preferably Fe(NO3)3·9H2O; the lithium source is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4, and CH3COOLi, preferably LiNO3; the doped metal source is an oxide, hydroxide, or inorganic salt containing at least one metal element from Mn, Co, Ni, Ca, Mg, Zr, Ni, and Cu, and can be MnSO4, CaCl2, NiSO4·6H2O, CoCl3, CoSO4·7H2O, CuSO4·5H2O, ZrSO4, MgCl2, etc., preferably CoSO4·7H2O.

[0038] In the above preparation method steps, the inert gas is one or more of nitrogen, argon, and helium, preferably nitrogen; the sulfur-containing precursor is at least one of elemental sulfur, sulfate, thiol, and sulfate ester, and can be soluble sulfur, insoluble sulfur, Li2SO4, lithium trifluoromethanesulfonate, lithium phenylsulfonate, ethyl mercaptan, dimethyl sulfate, etc.; the polymer monomer is at least one of aniline, pyrrole, thiophene, EDOT, acrylonitrile, acetylene, p-benzene, dopamine and its derivatives, wherein the amount of polymer monomer is calculated and determined based on the sulfur doped in the target positive electrode lithium supplement; the organic solvent is at least one of anhydrous ethanol, acetonitrile, propanol, tetrahydrofuran, carbon tetrachloride, carbon disulfide, DMF, DMAC, NMP, etc., preferably DMF, wherein the amount of organic solvent is not limited, as long as it can ensure that the materials are dispersed and do not agglomerate.

[0039] In the above preparation method, the high-temperature sintering temperature is 600-1000℃ and the sintering time is 2-40h; the polymerization reaction temperature is 80-300℃ and the reaction time is 2-20h.

[0040] The application of the above-mentioned positive electrode lithium supplement agent of the present invention is used to prepare lithium-ion batteries, preferably for preparing the positive electrode of lithium-ion batteries. Specifically, the positive electrode lithium supplement agent is mixed with the positive electrode active material to prepare a positive electrode sheet, and the amount of positive electrode lithium supplement agent added is 0.5-5% of the mass ratio of the positive electrode active material. The positive electrode active material is at least one of LiCoO2, LiFePO4, and NCM, preferably NCM811; the negative electrode active material is at least one of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon, and silicon-oxygen, preferably silicon-oxygen negative electrode.

[0041] The specific capacity test method of the above-mentioned positive electrode lithium replenisher of the present invention is as follows: the positive electrode lithium replenisher is used as the positive electrode active material to prepare a coin cell and conduct the first charge and discharge test, wherein the ratio of lithium replenisher:SP:PVDF is 8:1:1, the negative electrode is a Li sheet, the voltage range is 2.0-5.0V, and the current is 0.01-2C.

[0042] To provide a clearer and more detailed description of the positive electrode lithium replenishing agent, its preparation method, and its application provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0043] Example 1

[0044] In this embodiment, the positive electrode lithium supplementer is Li5Fe. 0.98 O4Co 0.02 The preparation method of @S-PTh includes the following steps:

[0045] According to the molecular formula Li5Fe 0.98 O4Co 0.02 The corresponding molar ratios of each element were Fe(NO3)3·9H2O, LiNO3 and CoSO4·7H2O, with LiNO3 in excess by 10%. All the substances were added to water and heated and stirred to form a uniform gel. The precursor powder was obtained by spray drying using a spray dryer.

[0046] The obtained precursor powder was sintered at 850℃ for 10 h in an argon atmosphere and then cooled in the furnace to obtain Li5Fe. 0.98 O4Co 0.02 ;

[0047] Add 20g Li5Fe to a 150mL polytetrafluoroethylene bottle 0.98 O4Co 0.02 0.2% high-purity sulfur and 1% polythiophene were added to DMF and dispersed evenly. The mixture was then polymerized in a high-pressure reactor and kept at 200℃ in a forced-air drying oven for 6 hours. After cooling, filtration, and drying to remove the solvent, Li5Fe was obtained. 0.98 O4Co 0.02 @S-PTh.

[0048] Example 2

[0049] In this embodiment, the positive electrode lithium supplementer is Li5Fe. 0.95 O4Co 0.05 The preparation method of @S-PAN includes the following steps:

[0050] According to the molecular formula Li5Fe 0.95 O4Co 0.05 The corresponding molar ratios of each element were Fe(NO3)3·9H2O, LiNO3 and CoSO4·7H2O, with LiNO3 in excess of 5%. All the substances were added to water and heated and stirred to form a uniform gel. The precursor powder was obtained by spray drying using a spray dryer.

[0051] The obtained precursor powder was sintered at 800℃ for 15 h in an argon atmosphere and then cooled in the furnace to obtain Li5Fe. 0.95 O4Co 0.05 ;

[0052] Add 20g Li5Fe to a 150mL polytetrafluoroethylene bottle 0.95 O4Co 0.05 0.5% lithium trifluoromethanesulfonate and 2% aniline monomer were added to DMF and dispersed evenly. The mixture was then polymerized in a high-pressure reactor and kept at 300℃ in a forced-air drying oven for 6 hours. After cooling, filtration, and drying to remove the solvent, Li5Fe was obtained. 0.95 O4Co 0.05 @S-PAN.

[0053] Example 3

[0054] In this embodiment, the positive electrode lithium supplementer is Li5Fe. 0.99 O4Co 0.01 The preparation method of @S-PPy includes the following steps:

[0055] According to the molecular formula Li5Fe 0.99 O4Co 0.01 The corresponding molar ratios of each element were Fe(NO3)3·9H2O, LiNO3 and CoSO4·7H2O, with LiNO3 in excess of 5%. All the substances were added to water and heated and stirred to form a uniform gel. The precursor powder was obtained by spray drying using a spray dryer.

[0056] The obtained precursor powder was sintered at 800℃ for 15 h in an argon atmosphere and then cooled in the furnace to obtain Li5Fe. 0.99 O4Co 0.01 ;

[0057] Add 20g Li5Fe to a 150mL polytetrafluoroethylene bottle 0.99 O4Co0.01 0.1% polysulfide and 1% polypyrrole were added to DMF and dispersed evenly. The mixture was then polymerized in a high-pressure reactor and kept at 300℃ in a forced-air drying oven for 2 hours. After cooling, the mixture was filtered and dried to remove the solvent, yielding Li5Fe. 0.99 O4Co 0.01 @S-PPy.

[0058] Comparative Example 1

[0059] Unlike Example 1, Comparative Example 1 prepared pure lithium ferrite Li5FeO4 without doping or coating.

[0060] The preparation method of Li5FeO4, the positive electrode lithium supplement in Comparative Example 1, includes the following steps:

[0061] Fe(NO3)3·9H2O and LiNO3 were weighed according to the molar ratio of each element corresponding to the molecular formula Li5FeO4, with LiNO3 in excess by 10%. All substances were added to water and heated and stirred to form a uniform gel. The precursor powder was obtained by spray drying using a spray dryer.

[0062] The obtained precursor powder was sintered at 850°C for 10 h in an argon atmosphere and then cooled in the furnace to obtain Li5FeO4.

[0063] Comparative Example 2

[0064] Unlike Example 1, Comparative Example 2 prepared Li5Fe 0.98 O4Co 0.02 No covering is performed;

[0065] Comparative Example 2: Lithium Supplementation Agent for Positive Electrode Li5Fe 0.98 O4Co 0.02 The preparation method includes the following steps:

[0066] According to the molecular formula Li5Fe 0.98 O4Co 0.02 The corresponding molar ratios of each element were Fe(NO3)3·9H2O, LiNO3 and CoSO4·7H2O, with LiNO3 in excess by 10%. All the substances were added to water and heated and stirred to form a uniform gel. The precursor powder was obtained by spray drying using a spray dryer.

[0067] The obtained precursor powder was sintered at 850℃ for 10 h in an argon atmosphere and then cooled in the furnace to obtain Li5Fe. 0.98 O4Co 0.02 .

[0068] Performance testing

[0069] Air stability and impedance evaluation

[0070] The positive electrode lithium replenishing agents obtained in Examples 1-3 and Comparative Examples 1-2 were used as positive electrode materials to prepare coin cells. The lithium replenishing agent: SP: PVDF = 8:1:1 was weighed and added to a mixing tank. An appropriate amount of NMP was added and mixed thoroughly to form a slurry. The slurry was then coated, dried, and rolled to obtain a positive electrode sheet. The positive electrode sheet was then assembled with a Li sheet to form a coin cell. Charge and discharge tests were performed on the cells, with a test current of 0.05C and a voltage of 2.5-4.5V. Two of the above positive electrode sheets were then taken from each cell and stacked to form a battery. After the electrolyte was fully impregnated, the impedance was tested.

[0071] In addition, the positive electrode lithium replenishment products obtained in Examples 1-3 and Comparative Examples 1-2 were exposed to an air atmosphere with a humidity of 50% for 24 hours, and then charged and discharged according to the same method as above. The test results are shown in Table 1.

[0072] Table 1. Specific capacity of the products before and after air exposure and stacked battery impedance in the examples and comparative examples.

[0073]

[0074]

[0075] As shown in Table 1, the positive electrode lithium replenishing agents obtained in Examples 1-3 of this invention all exhibited high air stability. After exposure to room temperature for 24 hours under air conditions with 50% humidity, their charge specific capacity remained >600mAh / g. In contrast, the positive electrode lithium replenishing agents obtained in Comparative Examples 1-3 all showed a charge specific capacity decrease of ≥70% after exposure to room temperature for 24 hours under the same humidity conditions. Moreover, the electrode impedance of the positive electrode lithium replenishing agents obtained in Examples 1-3 was much lower than that of the pure material, proving that the positive electrode lithium replenishing agent obtained using the technical solution of this invention can significantly improve the air stability and conductivity of the lithium replenishing agent.

[0076] Full battery performance evaluation

[0077] The positive electrode lithium replenishing agents obtained in Examples 1-3 and Comparative Example 1 were added to pouch cells, and the first charge-discharge efficiency and cycle tests were performed after capacity grading. The cycle test method was as follows: the positive electrode was commercial NCM811, the negative electrode was commercial silicon suboxide, the battery capacity was 5.0Ah, the cutoff voltage was 2.8V-4.2V, and the capacity retention rate was measured after 200 cycles at 0.5C / 1C. The test data are shown in Table 2.

[0078] Table 2 shows the battery cycle performance of the pouch cells from Examples 1-3 and Comparative Example 1.

[0079]

[0080] As shown in Table 2, the battery cycle performance test results of the soft-pack batteries from Examples 1-3 and Comparative Example 1 demonstrate that the technical solution of this invention can effectively improve battery stability. In Examples 1 and 3, under high temperature and pressure, a portion of the sulfur / polymerized sulfur copolymerizes with the conductive polymer to form a conductive framework with sulfur-containing end groups, while another portion self-polymerizes into polysulfides. When the polysulfides come into contact with the electrolyte, they react chemically with the carbonate solvent (such as EC) in the electrolyte to form a PEO-like structure (-O-(CH2CH2O)). n -CH2CH2S x Lithium trifluorosulfonate (Li) can be used as a CEI film component to cover the electrode surface, reducing the contact between the cathode and the electrolyte, and minimizing the catalytic effect of the cathode material on the electrolyte. This improves the high-voltage resistance of the electrolyte and enhances the long-cycle performance of the battery. In Example 2, lithium trifluorosulfonate is directly introduced. During the polymerization of polymer monomers, it is adsorbed in the network of conductive polymers in the form of small particles. During battery charging, it acts as a carrier for Li ion transport, improving the lithium removal energy of the lithium replenishing agent. The delithiated electronegative groups are adsorbed on the surface of the cathode material and recombine with Li or other film-forming components of the electrolyte to protect highly active sites and reduce electrolyte side reactions.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode lithium supplement, characterized in that, Includes the following steps: Iron source, lithium source and doped metal source are added to water in a certain proportion to form a uniform gel, and then the precursor powder is obtained by spray drying using a spray dryer. The precursor powder is sintered at high temperature under inert gas conditions to obtain lithium iron ferrite core, wherein the high temperature sintering temperature is 600-1000℃ and the sintering time is 2-40h. The lithium iron ferrite core powder, sulfur-containing precursor, polymer or polymer monomer are added to an organic solvent and polymerized in a high-pressure reactor. After filtration and drying to remove the solvent, a positive electrode lithium replenishing agent is obtained. The positive electrode lithium replenishing agent comprises a core containing lithium replenishing material and a coating layer covering the core containing lithium replenishing material. The core containing lithium replenishing material is doped or undoped lithium iron ferrite. The coating layer is a conductive polymer containing a sulfur-containing loading material, which is uniformly dispersed in the conductive polymer. The content of the sulfur-containing loading material is 0.01-1 wt% of the positive electrode lithium replenishing agent. The sulfur-containing loading material is at least one of elemental sulfur, polymerized sulfur, or sulfur-containing oxides, inorganic salts, organic salts, esters, and sulfur-containing polymers. The content of the conductive polymer is 0.5-10 wt% of the positive electrode lithium replenishing agent. The molecular formula of the positive electrode lithium replenishing agent is Li5Fe. 1-x O4M x @S / P, where M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Ti, and Al, 0 ≤ x ≤ 0.5; S is a sulfur-containing loading material; and P is a conductive polymer containing a conjugated structure.

2. The method for preparing the positive electrode lithium supplement according to claim 1, characterized in that, The conductive polymer is a conductive polymer containing a conjugated structure, and the conductive polymer is at least one of polyaniline and its derivatives, polypyrrole and its derivatives, polythiophene and its derivatives, PEDOT and its derivatives, polyacrylonitrile and its derivatives, polyacetylene and its derivatives, poly(p-phenylene) and its derivatives, and polydopamine and its derivatives.

3. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, The iron source is at least one of Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3•9H2O, FeCl3, and FeSO4. The lithium source is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4, and CH3COOLi; The doped metal source is an oxide, hydroxide, or inorganic salt containing at least one metal element selected from Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, and Al.

4. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, The molar ratio of the iron source to the lithium source is (5.0~7.0):

1.

5. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, The inert gas is at least one of nitrogen, argon, and helium.

6. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, The sulfur-containing precursor is at least one of elemental sulfur, sulfate, thiol, and sulfate ester; The polymer monomer is at least one of aniline and its derivatives, pyrrole and its derivatives, thiophene and its derivatives, EDOT and its derivatives, acrylonitrile and its derivatives, acetylene and its derivatives, p-benzene and its derivatives, and dopamine and its derivatives. The organic solvent is at least one of anhydrous ethanol, acetonitrile, propanol, tetrahydrofuran, carbon tetrachloride, carbon disulfide, DMF, DMAC, and NMP.

7. The method for preparing the positive electrode lithium replenishing agent according to claim 1, characterized in that, The polymerization reaction temperature is 80-300℃, and the reaction time is 2-20h.

8. The application of the positive electrode lithium supplement prepared by the method according to claim 1 or 2, characterized in that, The positive electrode lithium replenishing agent is used to prepare the positive electrode of a lithium-ion battery. The positive electrode of the lithium-ion battery includes the positive electrode lithium replenishing agent and the positive electrode active material, and the amount of the positive electrode lithium replenishing agent added is 0.5-5% of the mass ratio of the positive electrode active material.

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